Diterpenes from marine opisthobranch molluscs

Marine opisthobranchs represent a very interesting source of bioactive natu ral products, which exhibit an extraordinary variety of chemical structures . Opisthobranchs are naked molluscs, apparently unprotected by the physical constrain of a shell. In spite of this, they appear to be free of predatio n. Their survival is assured by a series of alternative defensive strategie s which include the use of chemicals. These bioactive compounds, which are often localized in selected parts of body and in the defensive mucous secre tion, can be derived from the diet or de novo biosynthesized. Terpenes represent the major group of secondary metabolites isolated from o pisthobranchs. Most of these compounds show both interesting biological pro perties and unique chemical structures. In particular, diterpenes include s ome of the most interesting examples of bioactive molecules. This review covers the chemistry of diterpenes from marine opisthobranchs, until approximately 1999. Isolation, synthesis and biosynthesis are separat ely discussed throughout the paper. Relevant data regarding biological acti vities are also reported.